Electromagnetic deflection display system including dual mode deflection amplifiers and output power limited supplies

ABSTRACT

An electromagnetic deflection display system for both random stroke and raster displays provides larger, faster and brighter displays with reduced power consumption and physical size. Dual mode deflection amplifiers having independent linear and slew characteristics provide reduced slewing time without any significant increase in power consumption and system power is limited to a predetermined average value to reduce system size and weight.

United States Patent 1 3,887,829

Owens, Jr. June 3, 1975 [54] ELECTROMAGNETIC DEFLECTION 3,628,083l2/l97l Holmes r r 3l5/27 TD DISPLAY SYSTEM lNCLUDlNG DUAL 3,786,303l/l974 Hilburn 3l5/27 TD MODE DEFLECTION AMPLIFIERS AND OUTPUT POWERLIMITED SUPPLIES Primary Examiner-Maynard R. Wilbur Assistant Examiner].M. Potenza [75] Inventor: Abner Owens Pompton Lakes Attorney, Agent, orFirmAnthony F. Cuoco; S. H.

Hartz [73] Assignee: The Bendix Corporation, Teterboro,

[57] ABSTRACT [22] Filed: June 28, 1973 An electromagnetic deflectiondisplay system for both [21] Appl' 374735 random stroke and rasterdisplays provides larger,

faster and brighter displays with reduced power con- 52 us. CL. 315/411;315/389; 315/403 sumption and P y Size- Dual mode deflection [51] Int.Cl. H01 29/70 Plifiers having independent linear and Slew Character- 5Field f Search 315 24 25 2 27 R 27 TD, istics provide reduced slewingtime without any signifi- 315/276 D 23 29 cant increase in powerconsumption and system power is limited to a predetermined average valueto reduce {56] References Cited System Size and Weight- UNITED STATESPATENTS 6 Claims, 8 Drawing Figures 3,602,768 8/197l Williams 3l5/27 TDUNREG 96 VOLTAGE 92 I34 souncz 9o PERCENT PEAK OUTPUT POWER INCREASINGDUTY CYCLE HEEI 4 MAX. FREQ. AND AMPLITUDE INPUT A Mr SATURATIONSATURATION m E OUTPUT DUAL MODE AMPLIFIER NON -DUAL MODE AMPLIFIERWAVESHAPES WAVESHAPES FIG. 4A FIG. 4 B

TATEVTFHJUM m5 3 8 i 829 SHEET 6 OUTPUT CURRENT vs TIME-EXCEEDEDPEAKPOWER A FOR +VL/\ I II F A FOR -v I OUTPUT CURRENT RECYCLING TRIGGERPOlNT 5' FOR -v \I W PEAK POWER B'FOR +v A L] I C. OR fV COMPARATORHYSTERES IS FIG. 6

ELECTROMAGNETIC DEFLECTION DISPLAY SYSTEM INCLUDING DUAL MODE DEFLECTIONAMPLIFIERS AND OUTPUT POWER LIMITED SUPPLIES BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates generally todisplay systems and particularly to display systems withelectromagnetically deflected cathode ray tube random stroke and TVraster displays such as claimed in copending commonly assigned US.application Ser. No. 374,736 filed June 28, I973. More particularly,this invention relates to systems of the type described including dualmode deflection amplifiers such as claimed in copending commonlyassigned US. application Ser. No. 374,736 filed June 28, 1973 forreducing slewing time without significantly increasing power consumptionand power supplies which are output power limited for reducing quiescentsystem power consumption as well as the size and weight of the system asherein claimed.

2. Description of the Prior Art Of major concern in electromagneticallydeflected cathode ray tube (CRT) display systems is the significantincrease in power consumption with larger, faster and brighter displays.These items become even more critical with the highly sophisticatedairborne navigation displays required in modern, high speed aircraft.where size, weight and power are at a premium.

The choice of deflection type for a given display system is a functionof three major factors: (a) the CRT light output requirement, and hencethe final CRT anode voltage, (b) the deflection angle, which is afunction of the maximum available CRT length and packaging geometry, and(c) the maximum allowable power dissipation. The primary requirement forthe deflection amplifiers for an electromagnetically deflected CRT isthat of supplying accurately controlled currents to the deflectionyokes. For apparatus which serves this purpose reference may be had toU.S. Pat. No. 3.426245 issued Feb. 4, I969 to John F. Yurasek and AbnerOwens, .Ir. for a High Speed Magnetic Deflection Amplifier, and assignedto The Bendix Corporation, assignee of the present invention.

An additional area of concern is the slew rate of the deflectionamplifiers. Amplifier slew rate design criteria (which also affect peakpower requirements) are dictated primarily by display content and formatrequirements and may be relaxed by minimizing the amount of informationto be presented by the display at any one time. In this connectionreference may be had to US. Pat. application Ser. No. 112,358 filed Feb.9, I97! by Abner Owens, Jr. and Donald Weinstein for Means forConserving Energy During Line Retrace of a Raster Type Display. andwhich application is assigned to The Bendix Corporation. assignee of thepres ent invention.

The present invention describes a system including slewing means wherebypower may be significantly re duced for any type of display i.e.,periodic or aperiodic. The system includes fast slewing switching dualmode deflection amplifiers and output power limited power supplies toachieve the desired results with reduced power consumption and reducedweight and size.

SUMMARY OF THE INVENTION This invention contemplates an electromagneticdeflection display system wherein input signals from, for example, asymbol generator are applied to deflection amplifiers, and whichamplifiers drive X and Y deflection yokes of a CRT. The deflectionamplifiers are of the dual mode type having independent linear and slewmodes of operation and with three distinct stages, i.e. a preamplifierstage, a fast slew switching stage and an output stage. The amplifiersare powered by power supplies which operate at predetermined duty cycleswhereby the power to the system is at a predetermined average value. Thesystem features larger, faster and brighter display presentations whileachieving significant reduction in system power consumption and physicalsize.

The main object of this invention is to provide an electromagneticdeflection display system providing larger. faster and brighter displayswith significant reductions in total system power consumption andphysical size.

Another object of this invention is to provide an electromagneticdeflection display system of the type described for both random strokewriting and TV raster displays, and having dual mode deflectionamplifiers and output power limited power supplies, with system powerconsumption and weight and size significantly reduced.

Another object of this invention is to provide a system of the typedescribed including dual mode deflection switching amplifiers havingindependent linear and slew characteristics whereby the slewing time isre duced without a significant increase in power consumption.

Another object of this invention is to provide a system of the typedescribed including power supplies where the power to the system islimited to a predetermined average value to reduce the quiescent powerconsumption of the system and significantly reduce system, size andweight.

The foregoing and other objects and advantages of the invention willappear more fully hereinafter from a consideration of the detaileddescription which follows, taken together with the accompanying drawingswherein several embodiments of the invention are illus trated by way ofexample. It is to be expressly understood, however, that the drawingsare for illustration purposes only and are not to be construed asdefining the limits of the invention.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of anelectromagnetic deflection display system according to the invention.

FIG. 2 is an electrical schematic diagram of the dual mode switchingdeflection amplifiers shown generally in FIG. I.

FIG. 3 is an electrical schematic diagram showing a linear model of theamplifiers shown schematically in FIG. 2.

FIGS. 4A-4B are graphical representations showing waveforms at variouspoints of dual mode (FIG. 2) and non-dual mode deflection amplifiers,respectfully.

FIG. 5 is an electrical schematic diagram of the output power limitedlinear and slew power supplies shown generally in FIG. 1.

FIG. 6 is a graphical representation showing waveforms at various pointsof the power supply shown schematically in FIG, 5.

3 FIG. 7 is a graphical representation showing output powercharacteristics versus time of the power supply shown schematically inFIG. 5.

DESCRIPTION OF THE INVENTION With reference to FIG. 1, a symbolgenerator 2 provides X and Y cathode ray tube (CRT) deflection signalsand a Z bright-up signal. Symbol generator 2 is of the type described incopending US. application Ser. No. 152,927 filed on June 14. 1971 byKenneth 1. Ken clall et al, and assigned to The Bendix Corporation.assignee of the present invention It will suffice to say for purposes ofthe present invention that the X, Y and Z signals from symbol generator2 are applied to the appropriate circuits of a CRT 4 for providingsymbology on the face of the CRT in response to signals from an externalsource, and which symbology may be used for flight control purposes.

Signal X from symbol generator 2 is applied to a switching deflectionamplifier 6 and signal Y from the symbol generator is applied to asimilar switching de flection amplifier 8. Switching deflectionamplifiers 6 and 8 are of the type which will be hereinafter describedwith reference to FIG. 2. The switching amplifiers are powered by alinear power supply 10 providing voltages +V and V and a similar slewpower supply 12 providing voltages +V and V, Power supplies l0 and 12are of the type which will be hereinafter described with reference toFIG. 5.

The Z signal from symbol generator 2 is applied to a conventional typevideo bright-up amplifier 14. Amplifier 14 is powered by a conventionalpower supply 16.

Switching deflection amplifier 6 is connected to an X'axis deflectionyoke 18 of CRT 4 and switching de flection amplifier 8 is connected to aY-axis deflection yoke 20 of the CRT. Video bright-up amplifier I4 isconnected to an appropriate bright up electrode 19 of CRT 4. CRT 4 ispowered by a conventional high voltage power supply 13.

It will now be understood that the electromagnetic deflection systemshown in FIG. 1 is effective for both random stroke writing and TVraster displays. Amplifiers 6 and 8 are dual mode deflection amplifiershaving independent linear and slew characteristics, whereby the slewingtime may be significantly reduced as compared to a non-dual arrangement,with no significant increase in power consumption as will be herinafterexplained. Power supplies l0 and 12 are of the type whereby the outputpower of the system is limited to a prescribed average value thusreducing system quiescent power consumption of the deflection system tosignificantly reduce the size and weight of the system as will also behereinafer explained.

It will be understood that CRT display edge to edge slew time variesanywhere from 100 microseconds to l microsecond depending on (a) whetherthe display is random stroke writing/symbology or of the TV raster typeand (b) the display content and format. The above. of course, impliesnonstorage type displays with frame rates in the order of 50 Hz. to 60Hz. In random stroke type displays. as display content increases so mustthe slew rate. In the TV raster type display. slewing is the flybacktime, which increases with an increase in the number of TV lines perframe. In the dual mode deflection system of the present invention theslewing mode requirement is virtually independent of the linear moderequirement as will become evident.

Thus, with reference to FIG. 2 wherein an amplifier such as theamplifiers 6 and 8 will be described. the amplifier includes a preampstage 22, a switching stage 26 and an output or emitter follower stage28.

Preamp stage 22 includes a very wide band high gain operationalamplifier 30 having an input terminal 32 at which an input signal A isreceived through a resistor 34 and a grounded input/output terminal 36.Amplifier 30 has an output terminal 38 at which a signal 13 is provided.A feedback loop including a resistor 40 and a serially connectedvariable capacitor 42 is connected to input terminal 32 and to outputterminal 38 of ampli fier 30.

Output terminal 38 of amplifier 30 in preamp stage 22 is connected to aninput terminal 44 of a switching amplifier 46 in switching stage 26.Amplifier 46 includes a power terminal 48 connected to a slew powersupply, such as the power supply 12, (FIG. 1) for re ceiving voltage +Vand a power terminal 50 connected to power supply I0 for receivingvoltage -V Amplifier 46 includes an output terminal 52 at which a signalC is provided. Switching stage 26 includes transistors S4 and 60.

Output stage 28 includes transistors 56 and 58. The base element oftransistors 54 and are connected intermediate output terminal 38 ofamplifier 30 and input terminal 44 of amplifier 46. The base elements oftrain sistors 56 and 58 are connected to output terminal 52 of amplifier46. The emitter element of transistor 54 is connected to power terminal48 of amplifier 46 and the emitter element of transistor 60 is connectedto power terminal 50 of amplifier 46. The collector elements oftransistors 54 and 56 are connected one to the other and the collectorelements of transistors 58 and 60 are connected one to the other. Theemitter elements of transistors 56 and 58 are connected one to the otherand a signal D is provided at a point 62 intermediate said emitterelements.

Voltage +V from power supply 10 is applied through a steering diode 64to the collector elements of transistor 54 and 56 and voltage V, fromthe power supply is applied through a steering diode 66 to a pointintermediate the collector elements of transistors 58 and 60. Adeflection yoke such as the deflection yoke 18, 20 (FIG. 1) and shownfor purposes of illustration as yoke 18 includes a coil 70, a resistor71 and a current sampling resistor 72 connected in series. Coil isconnected to point 62. A feedback resistor 74 is connected intermediateresistor 34 and input 32 of amplifier 30 and is connected to a point 76intermediate resistors 71 and 72, and at which point 76 a signal E isprovided. Waveforms for signals A, B, C, D and E are shown in thegraphical illustration of FIGS. 4A-4B, and which figures will behereinafter referred to.

The band width of amplifier 30 is a function of overall display systemrequirements which may vary from 60 Hz. to It) MHZ. The feedback loopincluding resistor 40 and capacitor 42 around amplifier 30 controls theresponse shape with respect to yoke shape while maintaining high DCfeedback fro position stability. This is accomplished by adjusting theRC time constant of the feedback loop to cause a zero to occur at thepole caused by the yoke time constant. Therefore. during the linear modeof operation the deflection amplifier is extremely stable since yoke 18,which is a linearpassive element, and not the amplifier, will cause anatural roll off of 6DB per octave in the system. In the linear mode themaximum linear band width of amplifier 30 is essentially a function ofyoke inductance, the positive and negative power potentials and theinput voltage amplitude.

With reference to FIG. 3 which is a linear model of the deflectionamplifier shown in schematic form in FIG. 2, a relationship involvingthe pertinent parameters may be determined as follows:

Equation may be normalized for more general use as follows:

where; D iV R /R closed loop gain m input frequency w, yoke timeconstant (-3DB point) From equation (2) it can be seen that with (a OMis essentially equal to R /R; and the amplifier closed loop gain is inthe order of from 0.1 to 0.5 for this type of amplifier.

It will now be understood that as input frequency (m increases beyond(an and holding A constant, D rises to the power of 2. This is, ofcourse, due to the in duction reactance of yoke 18.

From FIG. 2 it can be seen that D is equivalent to the supply potentialsiV Therefore, the maximum linear large signal bandwidth of thedeflection amplifier is readily predictable, i.e. knowing the closedloop gain [i /R yoke time constant w, and setting A to maximum (usually:5 volts) with D :V. 11),, may be determined. For maximum linear smallsignal bandwidth one would simply adjust A to the smallest excusionapplicable to the specific system.

As the input frequency and amplitude go beyond the maximum linear largesignal bandwidth limits. the deflection amplifier as shown in FIG. 2 issaid to go into the slew or nonlinear mode. While slewing. the outputcurrent waveform of the amplifier no longer represents the input voltagewaveform, and the amplifier effec tively becomes open loop andsaturates.

FIG. 4A illustrates voltage waveforms within the dual mode deflectionamplifier of the invention (FIG. 2) while FIG. 4B shows the waveforms ofthe same amplifier with the switching stage 26 removed. Thus. with theswitching stage removed the slewing time is not independent of thelinear mode of operation but is dependent on the potential :V as shownin FIG. 4B. If the linear signal bandwidth requirement is low. tV willbe relatively low and the slew time will be long which may not bedesirable. Increasing iV to decrease the slewing time will increase thelarge signal bandwidth unnecessarily and, more significantly, increasethe system power consumption.

A typical situation in which the aforenoted is obvious is in thehorizontal sweep voltage of a TV raster display where the linear sweeptime is about 85% longer than the slewing or flyback time. In the dualmode deflection amplifier of the present invention, the potential iV ischosen for the maximum large signal bandwidth while the switched inputpotential :V which may be much higher than :V, is selected for theslewing time re quirements see (FIGS. 2 and 4A). Voltage :V isdetermined by the following equation.

:V LI/T. where L yoke inductance I I yoke current maximum deflection.center to edge T slew time required Referring to FIGS. 2 and 4A, thedual mode deflection amplifier such as the amplifiers 6 and 8 of theinvention operates as will be next described.

When input signal A exceeds the linear bandwidth and amplitude, the dualmode deflection amplifier ef fectively becomes open loop as heretoforeexplained. Preamp stage 22 then saturates going far beyond the designlinear region to provide waveform B in FIG. 4A. This action also causesstage 26 to saturate to the high switching voltage iV to providewaveform C. At the same time the output of the switching stage appliesvoltage il/ to the bases of the output stage transistors 56 and 58 andthe preamp saturation causes transistors 54 and 60 to saturate applyingil to the collectors of transistors 56 and 58 respectively. As thecollectors of transistors 56 and 58 rise to iV diodes 64 and 66 becomereverse biased and disconnect the linear power supply iV The rise andfall time of waveform E shown in FIG. 48 decreases significantly to thatshown in FIG. 4A. Using this technique, slew time may be reduced by aminimum of 5 times that of the non-dual approach without any increase insystem power as will now be understood.

The electromagnetic deflection display system and the dual modeswitching amplifier apparatus heretofore discussed offers a significantreduction in system power requirements. The power supply of theinvention which will be next described operates at predetermined dutycycles and provides still further reductions in system power andphysical size of the equipment involved.

The equipment involved will be described, for purposes of illustration,with reference to TV raster and random stroke writing type displaysystems such as used in aircraft head-up or head-down displays orsimulators. It will be understood that these systems imply a non-storagetype display with refresh rates in order of 60 Hz. further. in analyzingthese systems certain predictions can usually be made with respect tothe display formats. With TV raster display there is. of course, theraster format which is accurately predictable at any instant i.e., thelinear sweep in either the vertical or horizontal and the slew duringthe respective flybacks. The random stroke format is more difficult topredict except for the refresh rate. However, more often than not somegeneralities can be attributed to most random stroke displays other thanthe refresh rate. For example. in a random stroke system the CRTelectron beam will not stay positioned in one corner of the display formore than I millisecond. As a matter of fact. in most systems the CRTphosphor protection device will sense no motion within this onemillisecond period which could present a display problem. and the CRTbeam is turned off. Essentially, then. the length of time that the CRTelectron beam is along the outer perimeter of the display surface willdetermine peak power duration for the random stroke system. The sameanalysis may be made for the TV raster mode of operation. Thus, itappears that since peak power is required only for short periods ofmaximum deflection. and the power requirements decrease to much lowerthan peak for a larger portion of the frame time, it is desirable todevelop a power supply system to fulfill these requirements.

With this in mind, the power supply systems of the present inventionhave been designed with maximum output power equal to the average powerrequirements of the system. Thus. there is provided a significantreduction in quiescent power. heat generated, and system size andweight.

FIG. shows in substantial detail a power supply according to theinvention such as the power supplies shown generally in FIG. 1 anddesignated by the numbers 10 and 12, and wherein power supply 12providing signal iV will be described for purposes of illustration, withanother such power supply being required for pro viding signal -V Anunregulated dc. voltage source 80 shown in FIG. 5 provides a positivevoltage r) which is applied to an input terminal 82 of a currentamplifier 84, and provides a negative voltage which is applied to aninput terminal 88 of a correction amplifier 90. Correc' tion amplifier90 has other input terminals 92 and 94 and an output terminal 96connected to a control terminal 98 of current amplifier 84. Currentamplifier 84 has an output terminal 100 connected to a power sourceterminal 102 through a current sampling resistor 104.

Output terminal 100 of current amplifier 84 is connected to an inputterminal 106 of an integrating amplifier 108. An input terminal 110 ofamplifier 108 is connected to power output terminal 102. Amplifier 108has an output terminal 112 connected to an input terminal 114 of acomparator amplifier 116. Comparator amplifier 116 has an outputterminal 118 connected to input terminal 94 of correction amplifier 90.

Output terminal 100 of current amplifier 84 is connected to an inputterminal 120 of a zero sensor 122 and another input terminal 124 of zerosensor 122 is connected to power output terminal 102. Zero sensor 120has an output terminal 126 connected to a control terminal 117 ofintegrator 108.

A power supply return terminal 128 is connected to DC voltage source 86and serially connected resistors 130 and 132 are connected acrossterminals 102 and 128. input terminal 92 of correction amplifier 90 isconnected at a point 134 intermediate resistors 130 and 132. Integrator108, zero sensor 122 and comparator amplifier 116 are included in apower limit sensor designated generally by the number 136.

In operation, the voltage developed across current sampling resistor 104is a function of the current flowing through the resistor. This voltagewaveform is integrated by integrator 108 in power limit sensor 136.whose maximum rate is a function of how long the CRT electron beam is atmaximum deflection. If this time is exceeded. the integrator will reacha voltage level at which comparator 116 will trigger and command thepower supply to shut down. Each time the voltage across current samplingresistor 104 is zero as sensed by zero sensor 122, or at somepredetermined quiescent level, integrator 108 is reset to zero thuspreventing the integrator from reaching trigger levels during smallquiescent levels. Hysteresis of comparator 116 prevents instability oroscillations from occurring.

From the configuration shown in FIG. 5, it will be understood that powerlimit sensor 136 may be used as short circuit protection circuitry andthe system will keep recycling on a short circuit. Resistors 130 and 132and correction amplifier provide a positive feedback network as is shownin the figure.

For a deflection system such as shown in FIG. 1, there are four powersupplies (two power supplies 10 and two power supplies 12) such as thepower supply shown in FIG. 5, two for the linear mode and two for theslew mode. It will be understood that any number of power supplies, maybe used as well, depending on the specific format of the display. Thelinear power supplies will always be of the type described withreference to FIG. 5. However, if there are no system slew requirementsthe slew power supplies are not necessary. Also, in some systems theonly slew requirement is during the retrace or llyback of the horizontalsweep of the TV raster. and thus the slew mode is only required in thenegative direction and a power supply providing voltage V.,- is the onlyone necessary.

FIG. 6 illustrates waveforms for signals at various points of the powersupply described with reference to FIG. 5, and which signals aredesignated in FIGS. 5 and 6 as A, B and C. It should be noted fromwaveform A of FIG. 6, that relative average power is low and durationsof peak power are relatively small. Some typical values of peak outputratios are; for iV about 30% of peak and for :V about l6% of peak.

FIG. 7 is a graphical illustration showing the output powercharacteristics versus time of the power supply concept of theinvention. The curve of FIG. 7 basically follows the square law; theplateau at power output is a function of the duty cycle of the systemand as the duty cycle increases the curve moves in the direction of thearrow.

It will now be seen that the aforenoted objects of the invention havebeen satisfied. An electromagnetic deflection display system for bothrandom stroke writing and TV raster displays including dual modedeflection amplifiers (linear and slew) and output power limited powersupplies contribute to decreased power consumption and system weight andsize. The dual mode deflection amplifiers have independent linear andslew characteristics to provide reduced slewing time with no significantincrease in power consumption. The output power limited power supplysystem, in limiting system power to a predetermined average value.reduces the quiescent power consumption of the system and furtherreduces system size and weight.

Although but several embodiments of the invention have been illustratedand described in detail. it is to be expressly understood that theinvention is not limited thereto. Various changes may also be made inthe design and arrangement of the parts without departing from thespirit and scope of the invention as the same will now be understood bythose skilled in the art.

What is claimed is:

1. For use in an electromagnetic display system of the type includingdeflection display means and power sups ply means providing power forpowering the deflection display means. the power supply meanscomprising:

a voltage source for providing an unregulated voltage;

power supply output and return terminals connected across the voltagesource;

amplifier means connected intermediate the voltage source and theterminals;

means connected to the amplifier means for sampling the outputtherefrom;

sensor means for sensing the sampled output and for providing an outputwhen the sensed output is commensurate with a display means deflectiontime in excess of a predetermined maximum de flection time; and

the amplifier means connected to the sensor means and responsive to theoutput therefrom for rendering the power supply in an off condition, andsaid power supply operating at predetermined duty cycle with the outputpower at a predetermined average value.

2. Power supply means as described by claim 1,

wherein the amplifier means includes:

a current amplifier having an input terminal connected to the voltagesource, an output terminal connected to the power supply output terminaland a control terminal;

a correction amplifier having an input terminal connected intermediatethe voltage source and the power supply return terminal, another inputterminal connected to the sensor means and an output terminal connectedto the control terminal of the current amplifier.

3. Power supply means as described by claim 2,

wherein:

a pair of resistors are serially connected across the power supplyoutput and return terminals; and

the correction amplifier has yet another input terminal connected to apoint intermediate said serially connected resistors. 4. Power supplymeans as described by claim 1,

wherein:

the amplifier means includes a current amplifier having an inputterminal connected to the voltage source and an output terminalconnected to the power supply output terminal;

the sampling means includes a resistor connected intermediate thecurrent amplifier output terminal and the power supply output terminal;and

the sensor means is connected across the resistor.

5. Power supply means as described by claim 4,

wherein the sensor means includes:

integrator means having a maximum rate as a function of thepredetermined maximum deflection time, and connected across the resistorfor integrating the voltage across the resistor and for providing atriggering signal when the maximum deflection time is exceeded; and

comparator means connected to the integrator means and triggered by thetriggering signal therefrom for providing the sensor means output.

6. Power supply means as described by claim 1, whererin the sensor meansincludes:

a sensor connected across the resistor for sensing when the voltageacross the resistor is at a predetermined quiescent level and forthereupon providing an output; and

the integrator connected to the sensor and responsive to the outputtherefrom for being reset.

1. For use in an electromagnetic display system of the type includingdeflection display means and power supply means providing power forpowering the deflection display means, the power supply meanscomprising: a voltage source for providing an unregulated voltage; powersupply output and return terminals connected across the voltage source;amplifier means connected intermediate the voltage source and theterminals; means connected to the amplifier means for sampling theoutput therefrom; sensor means for sensing the sampled output and forproviding an output when the sensed output is commensurate with adisplay means deflection time in excess of a predetermined maximumdeflection time; and the amplifier means connected to the sensor meansand responsive to the output therefrom for rendering the power supply inan off condition, and said power supply operating at predetermined dutycycle with the output power at a predetermined average value.
 1. For usein an electromagnetic display system of the type including deflectiondisplay means and power supply means providing power for powering thedeflection display means, the power supply means comprising: a voltagesource for providing an unregulated voltage; power supply output andreturn terminals connected across the voltage source; amplifier meansconnected intermediate the voltage source and the terminals; meansconnected to the amplifier means for sampling the output therefrom;sensor means for sensing the sampled output and for providing an outputwhen the sensed output is commensurate with a display means deflectiontime in excess of a predetermined maximum deflection time; and theamplifier means connected to the sensor means and responsive to theoutput therefrom for rendering the power supply in an off condition, andsaid power supply operating at predetermined duty cycle with the outputpower at a predetermined average value.
 2. Power supply means asdescribed by claim 1, wherein the amplifier means includes: a currentamplifier having an input terminal connected to the voltage source, anoutput terminal connected to the power supply output terminal and acontrol terminal; a correction amplifier having an input terminalconnected intermediate the voltage source and the power supply returnterminal, another input terminal connected to the sensor means and anoutput terminal connected to the control terminal of the currentamplifier.
 3. Power supply means as described by claim 2, wherein: apair of resistors are serially connected across the power supply outputand return terminals; and the correction amplifier has yet another inputterminal connected to a point intermediate said serially connectedresistors.
 4. Power supply means as described by claim 1, wherein: theamplifier means includes a current amplifier having an input terminalconnected to the voltage source and an output terminal connected to thepower supply output terminal; the sampling means includes a resistorconnected intermediate the current amplifier output terminal and thepower supply output terminal; and the sensor means is connected acrossthe resistor.
 5. Power supply means as described by claim 4, wherein thesensor means includes: integrator means having a maximum rate as afunction of the predetermined maximum deflection time, and connectedacross the resistor for integrating the voltage across the resistor andfor providing a triggering signal when the maximum deflection time isexceeded; and comparator means connected to the integrator means andtriggered by the triggering signal therefrom for providing the sensormeans output.